Casting wheel



Jan. 8, 1963 A. A. LA FORGE 3,071,810

CASTING WHEEL Filed Jan. 26, 1960 United States Patent ()fifice3,071,810 CASTING WHEEL Arthur A. La Forge, Seal-rd, Del., assignor toE. I. du Pout de Nemours and Company, Wilmington, Del., a corporation ofDelaware Filed Jan. 26, 1960, Ser. No. 4,756 3 Claims. (Cl. 18-15) Thisinvention relates generally to the production of fiber-forming polymersand is directed more particularly to an apparatus useful in the coolingof freshly extruded molten structures.

A process for producing polymer ribbons suitable for conversion intoflake has been disclosed by Graves in U.S. Patent No. 2,289,774. Afterdrying, blending and other preparatory steps, such flake is usually fedinto the hopper of a melt-spinning apparatus. One of the majordiiiiculties involved in these known procedures has been the length oftime required for casting the extruded ribbon. In this respect, it hasalso been recognized that a faster casting cycle would lead'to theproduction of polymer having a moreuniform thermal history and generallyimproved quality.

The most important object of the present invention is to provide anapparatus with which the elapsed time of the casting cycle is reduced soas to decrease the over-all processing time and improve the quality ofthe polymer.

A further important object of the invention is the provision of anapparatus in which the cooling step is accomplishedby vaporization ofthe coolant on both sides of an extruded ribbon as the latter isadvanced away from the point of extrusion.

It is another objective of the present invention to increase thesurface-to-volume ratio of the cast ribbon and thereby eifect moreuniform and efficient cooling through its entire cross section. 7

With these and other objects in view, the apparatus of the inventioncomprises generally an extrusion head which discharges a ribbon ofmolten polymer to a casting wheel having a foraminous surface on which alength of the ribbon is supported as it advances away from the extrusionhead. Roller means are provided for pressing the ribbon against theforaminous surface and a spray assembly is located adjacent the wheelwith nozzles directed at both the under and outer sides of theforaminous surface.

Additional objects will become apparent in the specification whichfollows wherein reference is made to the accompanying drawing in which:

FIGURE 1 is a side elevational view, partially in section, of anapparatus made in accordance with the teachings of the presentinvention;

FIG. Q. is a vertical sectional view taken on line II II of FIG. 1; and

FIGS. 3 and 4 are detail views of the roller asesmbly shown in FIG. 1.

The melt extrusion apparatus embodiment chosen for illustration includesas components thereof an autoclave 10, a casting Wheel 12, a sprayassembly 14, a roller assembly '15, and a pair of stripper rollers 16,1-8. The autoclave is provided with a valved and slotted head 20 fromwhich a ribbon 22 of molten polymer is extruded under pressure.

One side of the Wheel 12 consists of a hub 24 and a plurality of spokes26 which are attached at their extremities to a rim 28. The other sideof the wheel is closed by an imperforate sidewall 30 which has acentrally located apertured reinforcement 32 and is attached at itsperiphery to a second rim 34. A strip 36 of foraminous material iscoextensive in width with the Wheel 12 and attached to the rims 28, 34.The strip 36 may be made, for example, of heavy duty square weave Wire3,0 71,8 1 0 Patented Jan. 8, 1963 cloth or screen. For molten nylon, an8-mesh screen material is suitable. Wheel 12 is rotated in the directionindicated by the arrow in FIG. 1 by a driven shaft 38 which passesthrough hub 24 and reinforcement 32. Shaft 33 is joined to hub 24 bysuitable key means (not shown).

Spray assembly 14 includes a manifold 40 from which a plurality ofconduits 42, 44- lead to the several nozzle devices. Conduits 42 eachcommunicate with a perforated straight length 46 which is spacedoutwardly from and generally parallel to the screen 36. Conduits 44 leadto a plurality of spray heads or nozzles 48 each of which is locatedadjacent the path of travel of spokes 26 and directed inwardly towardscreen 36, as shown in FIG. 2.

The roller assembly 15 is mounted on a cross bar extending between apair of pivotally mounted arms 52 which are spring-biased in thedirection, of Wheel 12. As shown in FIGS. 3 and 4, the roller assembly15 includes a plurality of discs 54 which are relatively rotatable andheld spaced apart by spacers 56. A central perforation in each disc 54is larger in diameter than the cross bar on which the discs and spacersare mounted.

In operation, the polymer-forming reaction takes place in autoclave 10-and ribbon 22 passes directly from extrusion head 20 to the surface ofwheel 12 where a suitable non-solvent coolant is applied to both sidesof the ribbon by the radially directed curtain sprays emanating fromnozzles 46, 48. After the molten polymer has started to cool and as theribbon is advanced on wheel '12, the discs of spring-biased rollerassembly 15 press the polymer more intimately into the screen 36 andalso corrugate the outer side of ribbon 22. Simultaneously, the insideof the ribbon is deformed or roughened by its engagement with screen 36.The term roughened as used herein is intended to be descriptive of thepermanent deformation which results when the underside of ribbon 22becomes partially embedded in screen 36 during the casting operation.The extent of this deformation is increased and enhanced by the actionof roller assembly 15 which, as mentioned previously, also functions tocorrugate or roughen the outer side of the ribbon. In this manner, thesurface-to-volume ratio of ribbon 22 is increased substantially. Thisincrease permits a corresponding increase in the effectiveness of thespray applied to the ribbon. The cooling rate is further enhanced by thefact that the underside of the ribbon is cooled by vaporization of thecoolant rather than by conduction through an imperforate sheet. Ribbon22 stays on wheel 12 for less than a complete revolution and iswithdrawn by the stripper rolls 16, 18 for further processing in themanner disclosed by Graves.

Wheel 12 and spray assembly 14 are enclosed by a shroud 58 which isattached to the saddle of a suitable support 60.

In the illustrated embodiment, there is but one roller assembly 15. Itis apparent that, under different circumstances, it may be desirable tohave a plurality of such assemblies or to vary its construction. Forexample, the discs 54 and spacers 56 could be replaced with a rotatablymounted, screen covered drum in which the screen is of the same ordifferent mesh as that which is used on wheel 12.

The improvements over the process of Graves involve the steps ofdeforming or roughening both sides of an extruded molten structure andsimultaneously cooling both sides by vaporization. The incorporation ofthese features into the Graves process facilitates a more rapid anduniform cooling of the ribbon as it is cast.

The apparatus disclosed herein has special utility in the production offiber-forming polymers since they not only permit a reduction in theelapsed time of the casting cycle but also result in a narrowerdistribution of the flake chip sizes. Thus, there are less time andcoarse flakes and the cutter may be adjusted so as to increase theaverage flake size with no reduction in quality. The improvements withrespect to the duration of the casting cycle can be attributed to thefact that both sides of the extruded ribbon are cooled by vaporizationrather than by conduction and to the fact the roughening of the underand outer sides of the ribbon produces an appreciable increase in itssurface-to-volume ratio.

It is apparent that many changes and modifications may be made in thedisclosed apparatus for casting molten polymers without departing fromthe spirit of the present invention which is therefore intended to belimited only by the scope of the appended claims.

I claim:

1. A melt extrusion apparatus comprising: an extrusion head throughwhich molten material is extruded in the form of a ribbon; a castingwheel having an open mesh peripheral surface on which a length of theribbon is supported as it advances away from said head; roller meansengaging said ribbon in said length and pressing it against saidsurface; and a spray assembly located adjacent said wheel, said assemblyincluding nozzle means directed at both sides of said supported length.

2. In a melt extrusion apparatus including an extrusion head throughwhich molten material is extruded in the form of a ribbon: a rotatablydriven casting wheel having a ribbon-advancing strip of screen materialattached thereto at its periphery; and a spray assembly located adjacentsaid wheel, said assembly including nozzle means directed at the innerand outer sides of said strip in the length thereof over which saidribbon is advanced.

3. The melt extrusion apparatus of claim 2 wherein said wheel has animperforate sidewall, a hub spaced from said wall, and a plurality ofspokes extending radially from the hub, said strip is attached to theperiphery of said wall and to the extremity of each spoke, and saidnozzle means directed at the inner side of said strip comprises aplurality of radially spaced spray heads located adjacent said spokes onthe opposite side thereof from said sidewall, said heads beingpositioned and adapted to discharge toward the length of said strip overwhich the ribbon is advanced.

References Cited in the file of this patent UNITED STATES PATENTS1,942,764 Miller Jan. 9, 1934 2,289,774 Graves July 14, 1942 2,437,492Allen Mar. 9, 1948 2,615,822 Hulbner Oct. 28, 1952 2,776,451 ChavannesIan. 8, 1957 2,776,452 Chavannes Jan. 8, 1957

1. A MELT EXTRUSION APPARATUS COMPRISING: AN EXTRUSION HEAD THROUGHWHICH MOLTEN MATERIAL IS EXTRUDED IN THE FORM OF A RIBBON; A CASTINGWHEEL HAVING AN OPEN MESH PERIPHERAL SURFACE ON WHICH A LENGTH OF THERIBBON IS SUPPORTED AS IT ADVANCES AWAY FROM SAID HEAD; ROLLER MEANSENGAGING SAID RIBBON IN SAID LENGTH AND PRESSING IT AGAINST SAIDSURFACE; AND A SPRAY ASSEMBLY LOCATED ADJACENT SAID WHEEL, SAID ASSEMBLYINCLUDING NOZZLE MEANS DIRECTED AT BOTH SIDES OF SAID SUPPORTED LENGTH.